1. Field of the Invention
This invention relates in general to surface treatments of metals, particularly to those for steels requiring exceptional wear resistance under heavy loads such as those imposed upon earth boring drill bit bearings.
2. Description of the Prior Art
It has long been known that the surfaces of metals such as steel may be treated with a variety of elements or compositions that combine with the constituents of steel to produce hard wear resistant surfaces. One of the known prior art treatments is carburization. Another is boronizing.
The bearing surfaces of rotatable cutters in earth boring drill bits are commonly carburized, hardened and tempered to increase their wear resistance. Such surfaces sometimes have regions of soft anti-galling material such as silver or silver alloy, as disclosed in U.S. Pat. No. 3,235,316. The mating surfaces of the opposing bearings shafts often include deposits of hard metal of cobalt based alloy of the "Stellite" series.
Boronizing of the bearing surfaces of earth boring drill bits has not heretofore been commercially successful, principally due to the brittle nature of the hard surfaces and their shallow depth.